1. Field of the Disclosure
The following is generally directed to tin oxide-based electrodes, and particularly compositions for forming industrial electrodes for use in glass melting applications.
2. Description of the Related Art
Commercial glass melting operations typically rely upon use of fossil fuels such as natural gas or oil. The use of electric energy is also possible either as an additional source of energy, as the main source of energy, or the sole source of energy as in an electric furnace. In the latter case, electric furnaces make use of refractory electrodes whose very high electrical conductivity allows direct heating of the glass by passing the current between electrodes directly through the glass. Such electrodes have been fairly well studied in the art. However, with the development of new technologies and increasing demand for high performance glass components, such as for utilization in flat displays including LCD and plasma displays, increasing demands have been placed upon the mechanical and optical performance of glasses, and in turn the performance of glass melting equipment.
In the context of electric furnacing operations, use has been made of various tin oxide-based electrode compositions, such as those detailed in U.S. Pat. No. 3,287,284 (commonly owned by the present assignee). While the technology described in U.S. Pat. No. 3,287,284 is decades old, development of new tin oxide electrode materials has been incremental, common of mature art areas, and U.S. Pat. No. 3,287,284 represents important state-of-the-art materials. As described, the tin oxide-based compositions include various components that assist in densification or resistivity. Among the various additives described, U.S. Pat. No. 3,287,284 utilizes a combination of copper oxide, zinc oxide, and antimony oxide. The components are on the one hand described in fairly broad compositional ranges, namely 0.1 to 0.5% copper oxide, 0.5 to 1.0% zinc oxide, and 0.7 to 1.2% antimony oxide, but on the other, actually only reduced to practice within fairly narrow ranges.
However, the composition disclosed in '284 was discovered to have low thermal stability and unstable firing shrinkage that made forming industrial grade (i.e., large sized) electrodes difficult. Accordingly, as disclosed in USSR Patent 833,830 the percentages of some additives were changed to include 0.05 to 0.2% CuO, 0.2 to 1.55% ZnO, 0.25 to 1.75% Sb2O3 to combat the thermal instability of the '284 composition. However, this composition was discovered to produce electrodes having unsuitable (high) electrical resistivities. Further modifications to the tin oxide-based compositions have been slow and have focused on balanced ratios of the additives in an attempt to reduce the undesirable effects. See, for example U.S. 2006/0261317 and U.S. 2006/0016223.
While certain working compositions described in the above noted disclosures have desirable properties, a need continues to exist in the art for improved tin oxide-based electrodes, such as those having improved stable electrical properties, density, thermal stability, corrosion resistance, and formability.